Mycorrhiza Inoculation and Soil-Available Phosphorus Modulate Phosphorus Acquisition Strategies of Alfalfa

The
comprehensive understanding of how arbuscular mycorrhizal fungi
(AMF) and phosphorus (P) application affect P uptake by alfalfa roots
is poorly understood. We analyzed the effects of AMF inoculation and
P application levels on the trade-offs and variations in P acquisition
strategies of alfalfa by assessing plant growth, root morphology,
organic acid contents, phosphatase activity, root transcriptome, and
soil P forms. AMF inoculation increased five organic acid contents
(glutaric acid, 3-hydroxymethylglutaric acid, gallic acid, 2-hydroxyphenylacetic
acid, and fumaric acid) and phosphatase activity synthesized by alfalfa
and secreted by the roots and hyphae, which activated soil Ca2-P, Fe-P, and organic P, promoting root growth for P absorption
and biomass. Without AMF inoculation, plant biomass, P accumulation,
and root growth increased with increasing P application, and organic
acid contents were higher at P20 and P40 (20 and 40 mg P kg–1 dry soil). AMF colonization and phosphatase played a crucial role
in P acquisition under P-limiting conditions.